Back light module having concave-down luminance distribution

ABSTRACT

Several optical mechanism designs for making luminance of the outer portion of a back light module to become higher than luminance of the inner portion of the back light module of the direct lighting type are disclosed in accordance with the present invention. The disclosed optical mechanism designs can be cooperated with each other to enhance the optical effect of the back light module. Additionally, the back light modules of the present invention are feasible for utilization in various scanners or liquid crystal displays.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to back light modules, and more particularly, to back light modules whose outer portion has higher luminance than inner portion thereof.

2. Description of the Prior Art

A back light module is one of the key components for the liquid crystal display (LCD) or the scanner. The back light module comprises light sources and other optical devices for reflecting or refracting light to provide uniform light output. The light source of the back light module is typically a cold cathode fluorescent lamp (CCFL) or a light emitted diode (LED). In general, the back light module can be divided into two groups, the edge lighting type and the direct lighting type. The two groups are categorized by the positions of the light sources thereof.

In the conventional art, the main concept of designing both the edge lighting type and the direct lighting type is to ensure uniformity of the light output from the back light module, i.e., the luminance distribution of the back light module is uniform. Unfortunately, such a design concept may negatively affect the performance of some applications.

For example, suppose that a conventional back light module having uniform luminance distribution is employed in a scanner as a back light source required for scanning transparencies, and positive or negative films. The brightness of the outer portion of a scanned image received by an optical module of the scanner is usually lower than the brightness of the inner portion of the scanned image due to the optical characteristics or mechanical designs of the optical module. For these reasons the scanning quality of the scanner is thereby reduced.

SUMMARY OF THE INVENTION

An exemplary embodiment of a back light module of direct lighting type is disclosed comprising: a light emitting device for emitting light, wherein an outer portion of the light emitting device with respect to an axis has higher luminous intensity than an inner portion of the light emitting device; a diffuser positioned on a side of the light emitting device for diffusing light; and a reflecting device positioned on another side of the light emitting device for reflecting light emitted from the light emitting device to the diffuser.

Another exemplary embodiment of a back light module of direct lighting type is disclosed comprising: a light emitting device for emitting light; a diffuser positioned on a side of the light emitting device for diffusing light; and a reflecting device positioned on another side of the light emitting device for reflecting light emitted from the light emitting device to the diffuser; wherein the outer portion of the reflecting device has higher reflectivity or larger reflecting area than the inner portion of the reflecting device.

Thereto, another exemplary embodiment of a back light module of direct lighting type is disclosed comprising: a light emitting device for emitting light; a diffuser positioned on a side of the light emitting device for diffusing light, wherein the outer portion of the diffuser has higher light transmittance than the inner portion of the diffuser; and a reflecting device positioned on another side of the light emitting device for reflecting light emitted from the light emitting device to the diffuser.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram of a back light module of the direct lighting type according to one embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a luminous intensity distribution of a lamp of FIG. 1 according to one embodiment of the present invention.

FIG. 3 is a diagram showing different embodiments of the light emitting device of the back light module of FIG. 1 in accordance with the present invention.

FIG. 4 is a simplified diagram of a back light module of the direct lighting type according to another embodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1, which shows a simplified diagram of a back light module 100 of the direct lighting type according to one embodiment of the present invention. The back light module 100 comprises a light emitting device for emitting light. In this embodiment, the light emitting device is implemented with a first lamp 112 and a second lamp 114. In addition, the back light module 100 further comprises a diffuser 120 positioned on a side of the light emitting device for diffusing light, and a reflecting device positioned on another side of the light emitting device for reflecting light emitted from the light emitting device to the diffuser 120. In this embodiment, the reflecting device comprises a housing 130 and a reflector 140. As shown in FIG. 1, the reflector 140 is positioned between the light emitting device and the housing 130.

In one embodiment, the light emitting device is purposefully designed to increase the luminance of the outer portion of the back light module along an axis 10. For example, each of the first and second lamps 112 and 114 can be implemented with a lamp whose outer portion along the axis 10 has higher luminous intensity than the inner portion thereof.

For example, FIG. 2 illustrates a luminous intensity distribution of the first lamp 112 of the light emitting device according to one embodiment of the present invention. As shown, in this embodiment, the outer portion 112A and 112B of the first lamp 112 along the axis 10 have higher luminous intensity than the inner portion 112C of the first lamp 112. This configuration results in the two ends of the diffuser 120 receiving more light than the middle portion (i.e., the inner portion) of the diffuser 120. As a result, the luminance of the outer portion of the back light module 100 along the axis 10 is higher than the luminance of the inner portion thereof, i.e., the back light module 100 has a concave-down luminance distribution. In practice, the second lamp 114 of the light emitting device may have the identical luminous intensity distribution as the first lamp 112. Additionally, each of the first and second lamps 112 and 114 may be a cold cathode fluorescent lamp (CCFL).

In the foregoing embodiment, the light emitting device is implemented with two lamps. This is merely an example rather than a limitation of the present invention. For example, FIG. 3 shows three different embodiments of the light emitting device of the back light module 100 in accordance with the present invention. In implementations, the light emitting device of the back light module 100 may be a lamp having a bended shape such as a U-shape lamp 310 shown in FIG. 3. The U-shape lamp 310 can be implemented with a cold cathode fluorescent lamp (CCFL). A light emitting device 320 shown in FIG. 3 is an alternative embodiment. As shown, the light emitting device 320 comprises a straight lamp 322 (e.g., a straight CCFL) and a plurality of luminance units 324 for enhancing the luminous intensity of the outer portion of the light emitting device 320. The plurality of luminance units 324 can be a plurality of electro luminances (ELs), a plurality of light emitted diodes (LEDs), or a combination of the two. A light emitting device 330 shown in FIG. 3 is another embodiment. The light emitting device 330 is composed of a plurality of luminance units 332. In practice, the plurality of luminance units 332 can be a plurality of ELs, a plurality of LEDs, or a combination of the two. It can be appreciated by those of ordinary skill in the art that the luminous intensity of the outer portion of the emitting device 330 along the axis 10 can become higher than the inner portion of the light emitting device 330 by properly adjusting the arrangement (i.e., spacing) or density of the plurality of luminance units 332.

Please note that the light emitting device of the back light module 100 can also be implemented with other design choices. In addition, the number of light emitting devices employed in the back light module 100 is not a restriction of the present invention, i.e., two or more than two sets of light emitting devices may be employed as the light source in the back light module 100.

In the previous embodiment, the back light module 100 enhances the luminance of the outer portion thereof by utilizing the light emitting device whose outer portion has higher luminous intensity than the inner portion. In practice, the back light module 100 can obtain the same optical characteristic by adopting other optical mechanisms.

For example, the luminance distribution of the back light module 100 can be adjusted by modifying the design of the diffuser 120. In another embodiment, the diffuser 120 of the back light module 100 has non-uniform light transmittance distribution. Specifically, the diffuser 120 of this embodiment is purposefully designed such that the light transmittance of the outer portion of the diffuser 120 along the axis 10 is better than that of the inner portion thereof. As a result, the back light module 100 can obtain the same optical characteristic as the foregoing embodiments, i.e., the luminance of the outer portion of the back light module 100 along the axis 10 is higher than the luminance of the inner portion.

In another embodiment, the reflecting area of the outer portion of the reflector 140 is designed to be larger than the reflecting area of the inner portion of the reflector 140. Accordingly, the outer portion of the reflector 140 has better reflecting performance than the inner portion. This exposes the outer portion of the diffuser 120 to more light thereby enhancing the luminance of the outer portion of the back light module 100. Alternatively, the reflectivity of the outer portion of the reflector 140 can be designed to be higher than the reflectivity of the inner portion to reach or enhance the above optical effect.

FIG. 4 is a simplified diagram of a back light module 400 of the direct lighting type according to another embodiment of the present invention. The back light module 400 is similar to the above-mentioned back light module 100. Therefore, components that have the same implementations and operations are labeled the same. A difference between the back light module 400 and the back light module 100 is that the back light module 400 utilizes two reflectors 440 and 450 to replace the single reflector 140 of FIG. 1. As shown in FIG. 4, the two reflectors 440 and 450 are positioned between the light emitting device and the housing 130 with each corresponding to one of two ends of the light emitting device. In this embodiment, the light emitting device is implemented with the lamps 112 and 114. The two reflectors 440 and 450 are arranged for reflecting light emitted from the two ends of the light emitting device to the diffuser 120. The function of the two reflectors 440 and 450 is substantially the same as the reflector 140 of FIG. 1. In other words, the two reflectors increase light emitted to the outer portion of the diffuser 120 so that the outer portion of the back light module 400 has higher luminance than the inner portion thereof.

In practice, the housing 130 can be coated with reflective materials on an inside surface (e.g., a surface facing toward the light emitting device) to become a reflecting housing. For causing the luminance of the outer portion of the back light module 100 or 400 to be higher than that of the inner portion thereof, the reflective materials coated on the inside surface of the housing 130 can be designed to be a pattern that has two broad outer portions and a narrow inner portion. In another embodiment, the middle portion of inside surface of the housing 130 in which corresponding to the inner portion of the light emitting device is coated with a low reflective material while the outside portion of the inside surface corresponding to the outer portion of the light emitting device is coated with another material having a relative high reflectivity. Generally, as long as the outer portion of the reflecting housing 130 has higher reflectivity or larger reflecting area than the inner portion of the reflecting housing 130, the back light module can obtain the same or similar optical characteristic as the previous embodiment. As a result, the reflector 140, 440 or 450 can be omitted thereby reducing the cost of the back light module.

Note that, the different optical mechanism designs mentioned above can function independently or co-operate with each other to enhance the optical effect.

The disclosed back light module of the direct lighting type can be utilized as the back light source for various scanners and LCDs. For example, the back light module disclosed in accordance with the present invention can be applied in a scanner capable of scanning transparencies, and positive or negative films. The back light module disclosed in accordance with the present invention will significantly improve the fall off problems of the optical module caused by the optical characteristics or mechanical designs of the optical module.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

1. A back light module of direct lighting type comprising: a light emitting device for emitting light, wherein an outer portion of the light emitting device with respect to an axis having higher luminous intensity than an inner portion of the light emitting device; a diffuser positioned on a side of the light emitting device for diffusing light; and a reflecting device positioned on another side of the light emitting device for reflecting light emitted from the light emitting device to the diffuser.
 2. The back light module of direct lighting type of claim 1, wherein the light emitting device is a lamp having a bended shape.
 3. The back light module of direct lighting type of claim 2, wherein the lamp is a cold cathode fluorescent lamp (CCFL).
 4. The back light module of direct lighting type of claim 2, wherein the lamp is a U-shape lamp.
 5. The back light module of direct lighting type of claim 1, wherein the light emitting device comprises a plurality of electro luminances (ELs) or a plurality of light emitted diodes (LEDs).
 6. The back light module of direct lighting type of claim 1, wherein the light emitting device comprises a straight cold cathode fluorescent lamp (CCFL) and a plurality of electro luminances (ELs) or comprises a straight CCFL and a plurality of light emitted diodes (LEDs).
 7. The back light module of direct lighting type of claim 1, wherein the outer portion of the reflecting device has higher reflectivity or larger reflecting area than the inner portion of the reflecting device.
 8. The back light module of direct lighting type of claim 7, wherein the reflecting device comprises: a housing; and a reflector positioned between the light emitting device and the housing for reflecting light emitted from the light emitting device to the diffuser; wherein the outer portion of the reflector has higher reflectivity or larger reflecting area than the inner portion of the reflector.
 9. The back light module of direct lighting type of claim 7, wherein the reflecting device comprises: a housing; and two reflectors positioned between the light emitting device and the housing with each corresponding to one of two ends of the light emitting device, the two reflectors for reflecting light emitted from the two ends of the light emitting device to the diffuser.
 10. The back light module of direct lighting type of claim 7, wherein the reflecting device is a reflecting housing in which the outer portion has higher reflectivity or larger reflecting area than the inner portion.
 11. The back light module of direct lighting type of claim 1, wherein the outer portion of the diffuser has higher light transmittance than the inner portion of the diffuser.
 12. A back light module of direct lighting type comprising: a light emitting device for emitting light; a diffuser positioned on a side of the light emitting device for diffusing light; and a reflecting device positioned on another side of the light emitting device for reflecting light emitted from the light emitting device to the diffuser; wherein the outer portion of the reflecting device has higher reflectivity or larger reflecting area than the inner portion of the reflecting device.
 13. The back light module of direct lighting type of claim 12, wherein the reflecting device comprises: a housing; and a reflector positioned between the light emitting device and the housing for reflecting light emitted from the light emitting device to the diffuser; wherein the outer portion of the reflector has higher reflectivity or larger reflecting area than the inner portion of the reflector.
 14. The back light module of direct lighting type of claim 12, wherein the reflecting device comprises: a housing; and two reflectors positioned between the light emitting device and the housing with each corresponding to one of two ends of the light emitting device, the two reflectors for reflecting light emitted from the two ends of the light emitting device to the diffuser.
 15. The back light module of direct lighting type of claim 12, wherein the reflecting device is a reflecting housing in which the outer portion has higher reflectivity or larger reflecting area than the inner portion.
 16. The back light module of direct lighting type of claim 12, wherein the outer portion of the diffuser has higher light transmittance than the inner portion of the diffuser.
 17. A back light module of direct lighting type comprising: a light emitting device for emitting light; a diffuser positioned on a side of the light emitting device for diffusing light, wherein the outer portion of the diffuser has higher light transmittance than the inner portion of the diffuser; and a reflecting device positioned on another side of the light emitting device for reflecting light emitted from the light emitting device to the diffuser. 